This proposal describes a novel genetic method for mapping and experimentally controlling the neurons that are functionally connected within neural circuits. The approach used involves a modified plant-derived lectin carrier that is released in an activity-dependent fashion from presynaptic neurons, and is endocytosed by post- neuronal partners. The carrier lectin molecule has been modified from its native form to improve its efficiency of transfer and trafficking within the neuron. The carrier lectin is fused t various molecular cargoes, including a variety of fluorescent proteins, as well as epitope tags. Significantly, we use the carrier to transfer GV16, for the activation of UAS effector transgenes. To our knowledge this is the first example of a bipartite gene expression system that can be targeted to the members of a neural circuit. This method, which we term ITEM (Inducible Transneuronal Expression with Amplification), includes potent gene amplification. Using ITEM we can activate specific transgenes within synaptic partners, opening a new technology where the neurons of specific neural circuits can have specific transgenes activated in a genetic fashion. The project includes a series of proposed improvements to the technology, and functional tests as to its effectiveness as a tool to control gene expression in neural circuits.